Method of noiseless recording



Sept. 7, 1937. K. SCHWARZ METHOD OF NOISELESS RECORDING Filed June 26. 1955 NVENTOR KAR SCHWARZ i BY /fJ ATTORNEY Patented Sept. 7, 1937 maic? UNITED STATES PATTENT OFFICE Karl Schwarz, Berlin,

Germany, assignor to i Klangfilm G. m. b. H., Berlin, Germany, a corporaticn of Germany 3 Claims.

This invention relates to the' production of sound records that ;are free from background noise. To this end the sound is recorded throughout the entire length of the record with a straight zero line and the average transparency or transmission of the record strip intended for reproduction is varied with the sound Volume of the acoustic track. According to the invention this result is attained by projecting the image of a serrated or tooth-shaped mask or light stop on a light slit and moving this image in the direction of one of the tooth edges in` accordance to the sounds to be recorded and in the direction of the other tooth edge in accordance with the Volume or intensity of the sound.

The invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended f claims.

Referring to the drawing, v

Figs. la, lband lc' are explanatory diagrams relating to an explanation of the invention, and

Fig. 2 is a diagrammatic showing of a suitable embodirnent of the invention.

Referring to Fig. la, lil denotes a light slit in the plane of which the image' of a serrated stop is projected. This image is caused to move in the direction of tooth edge |2 in accordance with the acoustic vibrations to be recorded, and in the direction of 'tooth-edge |3 in accordance with a direct current which is obtained by rectification of part of the audio current and varies as the Volume of the sound. In other words, edge !3 is caused to oscillate parallel to the sense of edge !2 between limiting positions l3' and I3" as indicated by the broken line, this variation being in accordance With an amplitude which corresponds to the sound Volume of the acoustic action occurring at a given instant. By the said motion of edge 13, the illuminated length of slit is Varied so that upon a recording strip such as a motion picture film moved transversely of the slit the area shown shaded in Fig. lb` is blackened. The left hand boundary of this area corresponds to the sound wave while the right hand boundary is a line which contains no oscillations. This line is produced by tooth-edge 12` which, for practically complete control of edge |3 as shown in Fig.`1b, is almost in a position illustrate'd in Fig. la. With decreasing Volume of the sound the image II of the serrated stop is shifted in the direction of edge |3 in such a way that the tooth-edge !2, in the presence of zero. Volume will assume position 12' shown by broken line.

With increasing amplitude of the acoustic oscil- 4 lations to be recorded the tooth-edge !2 will be restored again from position' I 2' into the position indicated by solid lines in Fig. la. Fig. lc shows what blackening is produced upon the recording strip when the acoustic Volume is loW. When the acoustic Volume is low tooth edge i 3 will be shifted but slightly in the sense of the broken-line double headed arrow Hi, and the result is that the sound track upon the recording strip will be of but little amplitude. When the sound Volume is low tooth edge |2 is shifted from its initial position !2' which it occupies in the presence of Zero sound Volume only a small distance in the direction of the broken-line arrow !5 so that the right hand boundary of blackened portions of the recording strip is shifted in proportion to the lower sound Volume.

The zero line of the sound track, as can be seen from Figs. lb and lc is, however, the same whether the acoustic Volume is large or small. Recording, therefore, takes place with a straight Zero line irrespective of the sound Volumes. With increasing sound Volume of the sound record, the right hand boundary line of the blackened area is shifted approximately as far as the position indicated in Fig. lb. right hand boundary line, at constant sound volume, is parallel to the direction of film feed, though it forms a definite angle in reference to this direction upon the sound Volume decreasing or increasing.

If a record, as in Figs. lb' and lc; is copied or printed, then the mean transparency of the print which is suited for reproduction of the sound records will be so much smaller, the lower the recording sound Volume.

To make a sound track as in Figs. lb and la, recourse may be had to an arrangement as shown in Fig. 2. Referring to the latter, !5 denotes a serrated stop illuminated from the rear and imaged by way of a mirror I'l upon a slit-diaphragm lo. The image of the serrated stop, as in Fig. la is designated by ll. The objective lens which produces imaging of serrated stop !6 upon the plane of slit ID has been omitted in Fig. 2. Mirror l'l which may form a part of any appropriate type of oscillographic device upon which the audio impulses to be recorded are impressed oscillates about axis l'l', so that the image of serrated stop !6 moves in the direction of edges |2 in accordance with the sound waves. The serrated stop |6 itself is shifted in the sense of edges l3 by action of a rectified component of the audio current supplied to an electromagn'et In other words, the V [8 or other device suitable for moving the stop IS.

An arrangement according to this invention may also be so constructed that the serrated stop is stationary and that the mirror oscillating in accordance with the audio current is enabled. to undergo a further vib'ation about another axis I?" which forms with axis H', Fig. 2, the same angle as the two edges !2 and i3 of the serrated stop. such an arrangement may be produced by pivotally supporting the oscillographic device of which mirror H forms a part in a manner to permit movement in the required direction, as shown, for example in Egerton Patent 11395930, Nicolson Pat-emt 1,470,696, or Centano Patent 1,702,195.

The means to produce sound tracks finally could also be so designed that the serrated stop itself is capable of mobility in two directions axes IS' and s", being parallel to the two tooth edges, and that this serrated stop by way of an objective lens is directly imaged into the plane of slit IO.

The serrated stop may preferably have tooth edges enclosing an angle of With each other. This is conducive to lower electrical energy requirements for the oscillographic means controlling the mirror motions, as well as the means causing the shifting of the serrated stop itself. The serrated stop could also be furnished with teeth resembling those of a saw, that is, triangular, one edge of which is placed in the direction of travel of the recording film-strip, While the other one is positioned oblquely thereto.

I claim:

1. The method of sound recording which includes producing a light beam having angularly displaced edges, moving said. beam in a direction, parallel with one of said edges in accordance with said sound, and moving said beam in a direction paraliel to another of said edges in accordance With the Volume of said sound.

2. The combination of means defining a light slit, means for projecting on said slit a light beam having angularly displaced edges, audio current responsive means operable to move said beam in a direction parallel with one of said edges, and audio current Volume responsive means operabie to move said beam in a direction parallel with another of said edges.

3. The combination of means defining a light slit, means for projecting on said slit a triangularly-shaped light beam, current responsive means operable to move said beam in parallelism with one of said edges, and current Volume responsive means operable to move said beam in parallelism with another of said edges.

KARL SCHWARZ. 

